Lifting structural parts of buildings such as concrete floors has been done for many years and there are many ways in which such lifting is accomplished.
Most systems have hydraulic jacks to provide the lifting force and wedges or screws following the movement upward to insure continuous mechanical support. These systems are powerful and simple. This invention belongs in this category of lifting systems.
In a typical construction project utilizing this type of system there are usually a number of columns on which jacks are mounted. A serious problem in lifting large, heavy structures, especially concrete floor slabs and like structures, is that all lifting points must rise at exactly the same rate otherwise those structures become subjected to internal stresses and possible cracking or total failure.
Controlling the movement of lifting points in prior art has been done by simply placing a transit or builder's level in a strategic location from which incremental movement is observed. The observer controls the jacks by snubbing hydraulic valves that are placed within his reach. Another means of controlling movement is by having a special hydraulic pump deliver the same amount of oil to the jacks at each lifting point.
Both of these control methods are used extensively in the house raising and house moving business. They have also been used in liftslab construction, but in some cases with disastrous result because of inaccuracy in synchronization. A method now widely and successfully used in liftslab construction is a method patented by Marshall Long under U.S. Pat. No. 3,201,088. It has hydraulic jacks providing the lifting force. The oil feeding the jacks also feeds small cylinders which turn checknuts at each jacking point. Lifting is controlled in a manner that prevents the beginning of any new lifting cycle unless checknuts at all the lifting points have completed an incremental turn. The Long method is accurate and dependable. However, it has three distinct disadvantages: one is that the equipment is complex and expensive and consequently only economical in large projects. Another is that it has a power unit supplying oil to 20 to 30 jacks from one central location. A breakdown in the power unit shuts down the entire lifting operation. A third disadvantage is that the lifting units are placed on tops of columns. In multistory buildings this means that every time two stories have been lifted the equipment has to be removed to allow columns to be extended. Staging is time consuming and expensive. This invention seeks to eliminate these disadvantages.